Japanese eel Anguilla japonica do not assimilate nutrition during the oceanic spawning migration: evidence from stable isotope analysis

Abstract

During 2008 and 2009, a total of 12 adult Japanese eels Anguilla japonica were captured in the southern part of the West Mariana Ridge, the presumed spawning area. We compared the stable carbon and nitrogen isotope ratios (δ 13 C and δ 15 N) between the 'Mariana silvers' (terminal phase) and those of yellow and silver eels caught in rivers, lakes and coastal areas of Japan (initial phase). Profiles of stable isotope signatures between the initial and terminal phases were similar; both characteristically had a wide range for δ 13 C (-24.9 to -12.0 ‰ and -20.5 to -11.3 ‰ for the initial and terminal phases, respectively) and δ 15 N (6.5 to 18.4 ‰ and 9.0 to 18.1 ‰, respectively). Mesopelagic fishes, including several other anguillid species caught near the West Mariana Ridge, characteristically had a very narrow range of δ 13 C (-16.9 to -15.3 ‰) and a wide but lower range of δ 15 N (5.3 to 11.1 ‰) than the Japanese eels. The very similar profiles in stable isotopic signatures between the initial and terminal phase eels, distinct from those of Mariana mesopelagic fishes, indicate that Japanese eels do not assimilate nutrition from the marine environment during long (ca. 6 mo) spawning migration and retain the initial isotopic values of where they ceased feeding.

Variation of Lipids and Fatty Acids of the Japanese Freshwater Eel, <i>Anguilla japonica</i>, during Spawning Migration

“…This finding supports the assumption that A. japonica, which is carnivorous, migrates to spawning areas without feeding 16 because high n-6 PUFA levels are only found in some marine herbivorous fishes 6,7 .…”

“…Laboratory experiments support the fact that European eels are capable of swimming a distance of over 5500 km without resting and feeding 14 and the starving silver eels are able to reach their spawning grounds by using their stores of internal fat 15 . In the Pacific Ocean, the Japanese eel Anguilla japonica Temminck & Schlegel, Anguillidae may also depend on its store of fat for spawning migrations without feeding 16 because the alimentary tracts of silver eels are degenerated 17,18 . Recently, adult matured Japanese eels terminal phase have been caught in the West Mariana Ridge, which is its spawning area 16 .…”

“…In the Pacific Ocean, the Japanese eel Anguilla japonica Temminck & Schlegel, Anguillidae may also depend on its store of fat for spawning migrations without feeding 16 because the alimentary tracts of silver eels are degenerated 17,18 . Recently, adult matured Japanese eels terminal phase have been caught in the West Mariana Ridge, which is its spawning area 16 . An interesting comparison of the fatty acids of spawning-area eels terminal phase can be made with those of Japanese eels at the yellow and silver stages initial phase , which are collected in rivers and lakes and presumably influenced by terrestrial prey lipids Lake Ogawara 19 , and Amori River 20 .…”

First observations of the oceanic migration of Japanese eel, from pop-up archival transmitting tags

“…Therefore, migrating anguillid eels may typically swim between 100 to 499 m during the nighttime to avoid encountering such predators. It is clear, however, that the DVMs of anguillid eels are probably not related to feeding, because of the degeneration of the gastrointestinal tract, which has been observed in A. japonica in spawning condition (Tsukamoto et al 2011), and a lack of evidence of feeding during their spawning migration using stable isotope analyses (Chow et al 2010).…”

Optimization of salinity range for rearing glass eel Anguilla bicolor bicolor

“…A stadium of glass eel is the most vulnerable stage, which contributes to the high mortality if compared with stadia of elver and yellow eel (Durif & Elie, 2008;Okamoto et al, 2009;Okamura et al, 2009a,b;Chow et al, 2010;Clevestam et al, 2011). Its characteristic that migrates in large group from seawater to brackishwater causes the glass eel to be easily caught in large number in the estuary.…”